USES OF FUNGI. 65 



to two or three species of INTould. The effect of yeast seems to 

 depend upon the fiiet tliat whenever there is an interchange 

 of fluids on two sides of a living membrane, chemical change 

 takes place, and thus there are millions of points, when the 

 yeast-globules are diffused in the wort, at which fermentation 

 is carried on. The same observation applies to bread. The 

 different kinds of fermentation depend upon the degree of 

 temperature to which the fermenting body is exposed. The 

 globules of which yeast is composed retain their power of ve- 

 getation for mouths, and are capable of being preserved in a 

 dry state, in which form they are largely imported under the 

 name of German yeast. This compound is, however, some- 

 what capricious in its deportment. A. sudden blow, for in- 

 stance, is said to destroy its powers of germination. The 

 spawn of Moulds assumes sometimes a fleecy form, and in- 

 stead of globules consists of matted threads. In this state 

 it is the well-known Vinegar-plant, which has an extraor- 

 dinary effect in promoting acetic fermentation under proper 

 conditions of temperature. Little at present is known of 

 putrefactive ferments, but there is reason to believe that a 

 third condition of Moulds, consisting of extremely minute 

 bodies endowed "with molecular motion, is conducive to the 

 process. 



The other itses to which Fungi are put arc few, and mostly 

 of little importance. The German tinder, or Amadou of 

 commerce, so familiar to cigar-smokers, is made from the 

 pileus of Polyporus fomentarms, beaten out and steeped in 

 a solution of saltpetre. The pieces are often of consider- 

 able size, and when sewn together are sometimes fashioned 

 into coarse garments. It is also used for Moxa. Polyporus 

 officinalis was once extensively used in medicine as a purga- 

 tive, but it is seldom employed now. The Jcw's-ear (Plate 



